Reflex sight with large exit pupil



M 1949. L.. H. BROWN 2,464,209

REFLEX SIGHT WITH LARGE EXIT PUPIL Original FiledMarch 17,1944 2 Sheets-Sheet 1 1 March 15, 1949. L. H. BROWN REFLEX SIGHT WITH LARGE EXIT PUPIL 2 Sheets-Sheet 2 Original Filed March 17, 1944 mm llli lllllll gvwe/wbo LEE! H BREIWN,

Patented Mar. 15, 1949 UNITED STATES PATENT OFFICE Original application March 17, 1944, Serial No. 526,956. Divided and this application October 26, 1945, Serial No. 624,930

(Granted under the act of March 3, 1883, as amended April 30, 1928; 376 0. G. 757) 4 Claims.

The invention described herein may be manufactured and used by or for the Government for governmental purposes without the payment to me of any royalty thereon.

This invention relates to sights for guns.

This application is a division of my copending application, Serial No. 526,956, filed March 17, 1944, now Patent 2,453,697, November 16, 1948.

Among the objects of the invention is the provision of a reflector sight in which a large exit pupil may be obtained with a collimating lens system of small aperture.

Another object of the invention is to provide a reflex sight whose exit pupil is many times the area of the aperture of the collimating lens 01' collimating lens system, or many times the area of that part of the collimating lens or lens system through which light from the reticle is allowed to ass.

Still another object of the invention is the provision of a collimator gun sight which avoids the necessity of using large collimating lenses to obtain a large exit pupil or field of observation.

A further object of the invention is the provision of a reflecting collimator sight for guns which is compact in construction, and which may be symmetrical with reference to three axis at right angles to each other.

A further object of the invention is to provide means for apportioning a quantity of light over an area in several steps, without dispersion or substantial dispersion thereof.

Other objects will be appreciated from the detailed description below of embodiments of the invention.

In the accompanying drawings which illustrate several examples of gun sights constructed in accordance With the present invention:

Figure 1 shows in perspective the external appearance of one modification the gun sight and how it is used in sighting on a target.

Figure 2 is vertical cross section of the gun sight on the line 22 of Figure 1 with certain of the parts in elevation.

Figure 3 is a view partly in front elevation and partly in section on the line 3-3 of Figure 2.

Figure 4 is a cross section similar to Figure 2 of another modification of the invention and taken on the line 4-4 of Figure 5.

Figure 5 is a vertical section taken on the line 5--5 of Figure 4.

Figure 6 is a horizontal section taken on the line 66 of Figure 5.

Figure 7 is a cross section similar to Figure 2 of still another modification of the invention.

Referring specifically to the modification illustrated in Figures 1, 2 and 3 of the drawing, numeral I indicates a casing which is rectangular in cross section, and in which the collimating lenses 2, 3, reflecting prism 4, electric light bulb 5, light bulb housing 6 are mounted. Electric bulb 5 is enclosed within the housing 6 provided with an aperture 1 over which is placed the slide 8, which is carried in guides 9, 9 secured to the housing 6. A reticle is placed upon the slide 8 for illumination by light from the light bulb 5. The housing 6 is secured to the casing I in any suitable way, and preferably detachably. A reflector i9 is so disposed in relation to the light bulb that light emitted by the bulb is directed towards the reticle on slide 8. Slide 8 is removable from the guides 9 to enable replacement or substitution of reticles.

Above the collimating lenses 2, 3 and the housing 6 is placed a row of glass prisms I2, I3, I4, I5, I6 and I1. Prisms I2 and I! are triangular prisms and I3, I4, I5 and I6 are parallelepipedons or rhombohedrons. These prisms serially abut one against the other and are so shaped as to provide planes or interfaces of abutment 20, 2|, 22, 23 and 24 that are inclined at substantially 45 to the longitudinal axis of the row of prisms. On one of the abutting surfaces of each pair of abutting prisms, except the pair consisting of prisms I6 and I1, is formed a mirror of silver or of aluminum which partially transmits light and partially reflects light, in degrees or percentages described more in detail hereinafter. A full or opaque mirror is, however, formed on one of the abutting surfaces of I6 and I! forming the interface 26. The prisms I2, I3, I4, I5, I6 and i1, after the formation of said mirrors, are cemented together with Canada Balsam, so that there is a partially silvered mirror at each of the interfaces 26, 2I, 22 and 23, and a fully silvered mirror at interface 24. These mirrors which are parallel and inclined at 45 to the optical or longitudinal axis of the assembly are designated as mirrors 3|, 32, 33, 34 and 35.

Directly above the prisms I2, I3, I4, I5 and I6 is positioned a column or row of prisms 36, 31, 38, 39 and 46 which abut one against the other to provide parallel and inclined planes or interfaces 4|, 42, 43 and 44. Prisms 36 and 46 are triangular in cross section, while prisms 31, 38 and 39 parallelepipedons or rhombohedrons. These prisms are provided between their abutting surfaces, on one surface of each pair of abutting surfaces, with a mirror of silver or of aluminum which partially transmits and partially reflects light, each to the extent hereinafter described. The prisms, after silvering, are cemented together with Canada Balsam. The inclination of the abutting faces or mirrors is such as to form an angle of 45 with the optical axis of the column or row. For the purposes of reference these mirror surfaces are indicated by numerals 52, 53 and 54.

At one side of the column of prisms 35, 31, 38, 39 and 40, is positioned a transparent glass plate 5'! and a similar plate 58 is positioned on the opposite side of the said column. The said glass plates extend into the casing I where prisms I2, [3, I4, l5, l3 and I! are positioned between them. The plates 51 and 53 are cemented with Canada Balsam to prisms 33, 37, 33, 39 and 40 and to prisms l2, l3, l4, [5, I5 and I1 whereby the said prisms and the said plates constitute a unit which is insertable in casing l above the collimating lenses 2 and 3 and lamp' housing 6.

collimating lenses 2 and 3 and prism i are secured in casing I below the prism 13,,so that the light emerging from the lenses 2 and 3 is incident upon the first partial mirror 3 I.

Slide 8 and the reticle thereon is so positioned with relation to the collimating lenses 2 and 3 that the length of the optical path from the reticle to the collimating lenses is equal to the focal length of the lens combination consisting of lenses 2 and 3, whereby the light rays from the reticle after emerging from the collimating lenses are substantially parallel.

As appears in Figure 3, reflecting prism 4 is so positioned that light from the reticle or slide 8 is reflected into the collimating lenses, or lens combination.

The characteristics of the various mirrors which partially reflect and partially transmit light are now described. The total quantity of the light emerging from the collimating lenses is taken at 100%. Mirror 3| is so partially silvered as to transmit 20% of this total upwardly to prism 12,

whence it emerges and enters into prism 33. The

remaining 80% is reflected towards the mirror 32 which is so silvered as to reflect 25% thereof, or 20% of the original light, upwardly into prism 35. The 60% of the original light which remains is transmitted to mirror 33 which so silvered as to reflect 33%% of the said 60%, or 20% of the original light, upwardly into prism 36 and to permit 40% of the original light to be transmitted to mirror 34. Mirror 34, in turn, is so silvered that it reflects 50% of the light incident thereon, or 20% of the original light, upwardly into prism 35. The remaining 20% of the original light which is transmitted through mirror 34 proceeds to mirror 35 from which 100% of it, or 20% of the original light, is reflected upwardly into rism 35. The mirror 35 is, therefore, totally reflectmg.

It is to be noted that each of the five mirrors 3!, 32, 33, 34 and 35 is so silvered as to direct upwardly into prism 36, 20% of the 100% of light emerging from the collimating lenses 2 and 3. In this manner the parallel rays of light which diverged from the reticle are uniformly apportioned along the length of prism 33 and apportioned uniformly on mirror 5!. Thus, the five inclined mirrors 3|, 32, 33, 34 and 35 constitute means for apportioning a given quantity of light uniformly over an area, such as a reflecting surface 36, without substantial dispersion. This apportionment of the light may be considered as first occurring over a plane intersecting the 4 planes of mirrors 3 l, 32, 33, 34 and 35 at an angle of 45.

The sum of the five 20% portions of the original light incident upon mirror 5| now make up the quantity of light which emerges from the collimating lenses 2 and 3, neglecting, for the purpose of simplifying the description, absorption or losses which may have occurred.

New mirrors or mirror surfaces 5|, 52, 53 and 54 are so silvered as to partially reflect and partially transmit light incident thereon. Mirrors 5|, 52, 53 and 54 are each so silvered as to reflect a fraction of the total light entering prism 36 and to transmit the remainder. Such a reflected portion may be, for example 10% of the quantity of light entering prism 36. Thus, when said 10% is reflected by each mirror, each of said four mirrors must reflect respectively 10%, 11.1%, 12.5% and 14.3% of the percentage of the original light incident thereon. Thus inclined mirror 5!, 52, 53 and 54 constitute means for apportioning a quantity of light without substantial dispersion, over a plane, represented by the plane of plate 51 which is at an angle of 45 with the planes of the mirrors 5|, 52,53 and 54 in the illustrated embodiment of the invention.

The 60% of the total of the light which enters prism 33, which is not reflected by mirrors 5|, 52, 53 and 54 is transmitted upwardly out of the prism 40 or absorbed in a black coating applied to the top thereof.

The silver or aluminum coating of mirrors 5|, 52, 53 and 54 must be thin enough to enable the target to be seen therethrough when looking through the device as shown in Figure 1 when the plate 51 faces the observer.

Operation-The broken lines with arrow heads applied thereto indicate the path and apportion ment of a pencil of light rays starting at the reticle on slide 8, and which enters collimating lens combination 2, 3, symmetrically with respect to the principal axis of the said collimating lens combination. The pencil after passage through the collimating lens combination is constituted of parallel rays of light. The parallel rays are first incident upon the mirror 3|, and thereafter subsequently pass through each of partial mirrors 32, 33 and 34 and finally on to full mirror 35. At mirror 3!, 20% of the total quantity of the light in the pencil is transmitted upwardly into prism l2 and then into prism 36, and at each of mirrors 32, 33, 34 and 35, 20% of the total quantity of light in the original pencil is apportioned and "reflected upwardly into prism 36.

The light which emerged from the collimating lens combination 2, 3 has now been spread out and apportioned uniformly in a direction parallel to its direction of propagation. The light now proceeds in succession to and through mirrors 5|, 52, 53 and 54 which each apportion it by partial reflection and partial transmission, so that the light now becomes spread out and apportioned as indicated by the arrow heads 53 in Figure 2 in 'a direction at right angles to the direction inwhi'ch it was spread out by mirrors 3|, 32, 33, 34 and '35, or over an area, for example, on the plane of plate 51, forming an angle of 45 with theplanes of mirrors 5 I, 52, 53 and 54.

Referring now specifically to the modification illustrated in Figures 4, 5 and 6, the numeral 50 indicates a casing in which the various prisms and lenses are assembled. This casing is provided with a removable cover portion 6| at one end to permit insertion of the various elements within the casing. The upper part of the casing 5 is open at both sides to provide opposite windows 62 and 63.

A number of square converging collimating lenses are arranged in a row across the casing 60. Four of such lenses are illustrated in Figure 5 and indicated therein by numerals 64, 65, 66 and 61. These lenses are positioned in the casing 60 below the windows 62 and 63 and are held therein in any suitable manner. The converging lenses are contiguous and substantially in the same plane, with their principal axes substantially parallel.

A triangular reflecting prism 68 is secured in any suitable manner in the casing 60 below the lenses 64, 65, 66 and 61, and the reflecting surface of said prism is of sufficient extent to reflect light incident thereon to all four of said lenses. Prism 68 is advantageously located near the bottom of casing 60 and is secured over four openings 69 therein. The distance between the centers of these openings is equal to the distance between the centers of the four collimating lenses, whereby an opening corresponding to each lens is provided.

Four reticle plates I6 are cemented with Canada Balsam on the face of prism 68 that covers the openings 69, each plate being cemented on said face to register with one of said openings. Each plate I carries a reticle, each reticle being so located that light from the center thereof enters its corresponding collimating lens substantially along its principal axis. The reticles preferably lie in the interface formed by each plate I0 and prism 68.

A light housing II covers the openings 69 as shown in Figure 4, and is provided with flanges I2 which engage and slide in guides I3 to enable the light housing to be removed from casing 60, whereby solar light may be used to illuminate the reticles on reticle plates I0, when it is possible to employ this form of illumination.

Light housing II carries four electric light bulbs 14 which register with the four openings 69. A reflector I5 is provided for each light bulb. These lights provide illumination for the reticles on plates I0 when solar or daylight illumination is not used.

Four or more glass prisms BI, 82, 83, and 84 extend across the casing 60 above the four collimating lenses 64, 65, 66 and 61 and are arranged as a column or row in the same way that the prisms 36, 31, 38, 39 and 40 are arranged in the modification illustrated in Figures 1, 2 and 3. They are cemented together in the same way as the latter and in the interfaces 85, 86, 81 designated respectively as first, second and third, are provided mirror coatings or surfaces which partially reflect light. These mirrors are indicated by the numerals 9|, 92 and 93, 9| being designated as the first. However, in the modification of the invention illustrated in Figures 4, 5 and 6 the coatings of silver or aluminum have been so applied to the prisms as to give percentages of light reflectance and light transmission which are different from those given in connection with the modification illustrated in Figures 1, 2 and 3. Thus, in the modification illustrated in Figures 4, 5 and 6, there are three inclined reflecting mirrors 9|, 92 and 93 with the following light reflectin and light transmitting characteristics: mirror 9| reflects 33 /3% and transmits 66%% of the light incident thereon; mirror 92 reflects 50% and transmits 50% of the light incident thereon; and mirror 93 reflects 100% and transmits zero percent of the light incident thereon, Therefore, taking the light which enters prism 8| as 100%,

33%% of it is reflected at each of mirrors 9I, 92 and 93, as indicated by the dotted lines 94, and 96. These mirrors are inclined in the same way and to the same extent as the mirrors in the modification illustrated in Figures 1, 2 and 3. The prisms 8I to 84, inclusive, thus jointly form an optical sighting unit having plane parallel surfaces, the surface nearest the eye of the shooter, that is, the surface through which reiiectors 9!, 92 and 93 deflect light, being the rear ace.

The length of the optical path from each reticle on the reticle plates I0 to the collimating lenses 64, 65, 66 and 61 is equal to the focal length of these lenses, whereby the light rays which proceed from the reticles to the said lenses emerge substantially parallel from the latter.

In the modification of the invention illustrated in Figure 7 the simultaneously light transmitting and light reflecting mirrors are carried on inclined glass plates I00 instead of being positioned in intersurfaces between prisms as in Figure 4. A plurality of collimating lenses is also employed as in the modification illustrated in Figures 4, 5 and 6, one of the lenses being indicated by the numeral IOI in Figure 7. A reticle is located on reticle plate I02 which is illuminated by an electric light I03 provided with reflector I04. The reticle plate I02, light I03 and reflector I04 are contained within a housing I05 secured to casing I06. Casing I06 corresponds to casing 60 of the modification illustrated in Figures 4, 5 and 6, and housing I05 covers the opening I01 in the wall of said casing through which light passes from the reticle on plate I02 to inclined mirror I08 at the bottom of casing I06. There is a light and a reticle for each collimating lens IOI. The inclinationof the mirrors on inclined plates is the same as in the other modifications described above. Plates I00 are secured on brackets I09 carried on each end H0 of casing I06. Windows III and H2 are provided in the casing I06 above the collimating lenses, and correspond to windows 62 and 63 of the modification illustrated in Figures 4, 5 and 6.

In the modifications illustrated in Figures 4 to 7 inclusive, light proceeds from the reticles to the collimating lenses and then to the inclined simultaneously light transmitting and light reflecting surfaces 9|, 92 and 93 (of the modification illustrated in Figures 4, 5 and 6) and to the simultaneously light transmitting and reflecting surfaces on plates I00 (of the modification illustrated in Figure '7).

I claim:

1. In a gun sight, an optical sighting unit having plane parallel forward and rear surfaces through which a target may be viewed in aiming a gun upon which said sight is mounted, said unit comprising a plurality of stacked prisms rhomboidal in cross section in planes normal to said surfaces and extending in a first direction, the consecutive abutting parallel faces of said prisms being partially reflecting and making a dihedral angle of 45 with said direction to deflect light incident thereon through said rear surface, and illuminating means fixed with respect to said unit to project onto said abutting parallel faces, by rays parallel with said first direction, a plurality of reticle images in spaced side-by-side relation.

2. In a gun sight, a casing, an optical sighting unit disposed in said casing between aligned viewing openings in the opposite sides thereof, said unit forming spaced forward and rear plane parallel sighting surfaces through which a target may be viewed in aiming a gun on which said sight is mounted, said unit comprising a plurality of rhornbohedrons stacked in one direction parallel to said surfaces and having their faces parallel, abutting and inclined at 45 to said surfaces, each said face being partially reflecting, a plurality of lenses mounted in said casing in side by side relation to extend along one side of said unit with their principal axes parallel and intersecting said inclined reflecting surfaces at an angle of 45, and light sources carried by said casing and corresponding in number with said lenses, each source being adapted to project a beam of light through a corresponding lens onto said faces in succession, each said face acting to reflect through said rear surface, a substantially fixed percentage of the total light incident on the first of said faces.

3. In a reflex gun sight, an optical unit having plane parallel forward and rear surfaces through which a target may be viewed in sighting, said unit being formed of first and second prisms in the form of equal rhombohedrons having their abutting faces at 45 to said surfaces, and third and fourth triangular prisms abutting said first and second prisms, respectively, to complete the form of said unit as a right parallelepipedon, a plurality of collimating lenses mounted in sideby-side relation adjacent said unit and having their principal axes parallel and at 45 to the abutting faces of said prisms and passing substantially mid-way between said surfaces, means including a light source for projecting reticle images through each said lens, the abutting faces of said prisms being partially reflecting whereby a plurality of reticle images are projected in rows and columns through the rear surface of said unit, said abutting faces completely overlapping in the direction of said principal axes.

surfaces, a plurality of spaced reticle images in V side-by-side relation along said one face, whereby a plurality of reticle images are projected in rows and columns through the rear surface of said unit, said abutting faces substantially overlapping in the direction normal to said one face. LEO H. BROWN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 683,203 Grubb Sept. 24, 1901 1,318,292 -Kunz Oct. 21, 1919 1,456,427 Gorsky May 22, 1923 1,563,373 Kauch Dec. 1, 1925 1,688,606 Wright et a1. Oct. 23, 1928 2,390,439 Johnson Dec. 4, 1945 FOREIGN PATENTS Number Country Date 269,447 Germany Jan. 22, 1914 452,644 Germany Nov. 1'7, 1927 776,640 France Nov. 8, 1934 437,444 Great Britain Oct. 28, 1935 828,107

France i. Feb. 7, 1938 

